The Edge of the Abyss: Black Hole X Ray Evidence Quiz

If a photon is emitted near a massive object like a black hole, then it must expend energy to escape the gravitational pull. If energy is lost, then the frequency of the light decreases. If the frequency decreases, then the light shifts toward the red end of the spectrum. Therefore, this is gravitational redshift.

If a black hole is invisible, then we must look at the behavior of the matter around it. If that matter emits X-rays, shows relativistic distortions, and changes brightness very quickly (implying a small source), then it fits the model of a black hole. Therefore, A, B, and D are valid evidence.

If the outward pressure of the emitted light (radiation) equals the inward pull of gravity, then the accretion process reaches a balance. If this balance defines a theoretical maximum brightness for a given mass, then it is named after Sir Arthur Eddington. Therefore, it is the Eddington Limit.

If gas falls into a black hole, then it does not flow in a perfectly smooth stream. If the gas is turbulent and clumped, then different amounts of energy are released at different times. Therefore, the resulting X-ray signal varies in brightness, creating a "flicker."

If a black hole is in orbit with a normal star, then its gravity can strip the outer layers of that star. If that stolen gas spirals toward the black hole, then it forms a hot accretion disk. If that disk emits X-rays, then the system is classified as an X-ray binary. Therefore, the statement is true.

If gravity is stronger closer to the black hole, then the gas orbits at higher speeds. If the gas is moving faster and is more compressed near the center, then the friction and collisions become more intense. Therefore, the inner parts of the disk are much hotter than the outer parts.

If a global network of radio dishes acts as one giant telescope to see the silhouette of an accretion disk against the event horizon, then it is the EHT. If this project successfully imaged M87* and Sgr A*, then it provided direct visual confirmation. Therefore, the answer is Event Horizon.

If a black hole is rotating, then according to General Relativity, it "drags" the surrounding space-time with it. If space-time is being twisted, then the orbits of the gas in the accretion disk are affected. Therefore, frame-dragging is a result of the black hole's spin.

If we are looking specifically for X-rays, then the telescope must have mirrors and sensors designed for high-energy photons. If Chandra, XMM-Newton, and NuSTAR are dedicated X-ray missions, then they are the correct tools. Therefore, A, B, and D are the correct choices.

If nuclear fusion converts about 0.7% of mass into energy, then it is relatively efficient. If matter falling into a spinning black hole can convert up to 42% of its mass into radiation energy via the accretion disk, then gravity is the more efficient power source. Therefore, black hole accretion is the most efficient energy process known.

If a disk has ionized gas (plasma), then it generates strong magnetic fields as it rotates. If these magnetic fields become twisted and compressed at the poles, then they can accelerate particles outward at nearly the speed of light. Therefore, the interaction of magnetism and spin creates the jets.

If high-energy X-rays from the "corona" (a hot cloud above the disk) hit the cooler disk, they are reflected. If this reflection adds a specific bump to the energy spectrum around 20-30 keV, then it is known as the reflection hump. Therefore, the answer is Hump.

If the entire X-ray power of a galaxy can vary in a few minutes, then the source must be small enough for light to travel across it in that time. If the radius is only 30 km, then it fits the criteria for an extremely compact object. Therefore, the source must be a black hole or neutron star.

If there is a cloud of hot, diffuse gas near the center of the disk, then it is called the corona. If this region scatters lower-energy photons into high-energy X-rays through "Inverse Compton Scattering," then it is a major X-ray source. Therefore, the statement is true.

If matter falls toward a black hole, then it gains immense kinetic energy. If that matter crowds into a disk, then internal friction and compression convert that energy into heat. If the temperature reaches millions of degrees, then the black body radiation shifts from visible light to high-energy X-rays. Therefore, the heat generated by gravity causes X-ray emission.

If an accretion disk is a structure of orbiting gas outside the black hole, then it has a physical volume. If the event horizon is a mathematical boundary from which nothing can escape, then it is not a physical object or "surface." Therefore, the disk and the horizon are two distinct regions of space.

If the accretion disk is rotating at relativistic speeds, then the Doppler Effect applies to the emitted light. If a source of light moves toward the observer, then the waves are compressed. If the waves are compressed, then the wavelength decreases. Therefore, the light from the approaching side of the disk is blueshifted.

If general relativity defines a limit to how close matter can orbit a black hole before falling in, then there must be a "last" stable path. If this is the Innermost Stable Circular Orbit, then it is abbreviated as the ISCO. Therefore, the answer is ISCO.

If an iron atom emits a specific X-ray frequency, it should appear as a sharp line. If that atom is in a disk spinning near a black hole, then extreme gravity and high-speed motion stretch that line into a wide "wing" shape. Therefore, a broadened line is evidence of the extreme environment near a black hole.

If the event horizon is the point where the escape velocity exceeds the speed of light, then nothing (including X-rays) can escape from inside it. If we detect X-rays, then they must have been emitted by the hot gas before it crossed the horizon. Therefore, the X-rays we see come from the accretion disk outside.